You do understand, don't you that many of the people who post here, also post at other forums?

Since you say this is an integral, √(9-x²) / (x²) is NOT the problem statement: it has to be something like [itex]\int \sqrt{9- x^2}/x^2 dx[/itex].

Yes, with [itex]x= 3sin(\theta)[/itex] [itex]\sqrt{9- x^2}= 3\sqrt{1- sin^2(\theta)}= 3cos(\theta)[/itex]. Now, what is x2 in terms of [itex]\theta[/itex]. You need to replace that too. And what is dx? You need to write that in terms of [itex]\theta[/itex].